This invention refers to a unit intended to supply gasoline and air mixture to an internal combustion engine in special operating conditions, such as the operation at minimum speed, the start period, the operation as motor-brake and/or the acceleration.
In the normal operating conditions, namely when the engine runs at a sufficiently high and substantially constant speed, one or more elementary carburetors, each of which comprises a choke shaped as a venturi tube, a shutter and a jet supplied by a constant level fuel bowl, are suitable for supplying to an internal combustion engine a gasoline and air mixture sufficiently homogeneous in order to ensure a correct operation, with normal performances and consumption, and a combustion complete enough for avoiding an excessive pollution of the ambient. On the contrary, these conditions cannot be satisfied by elementary carburetors in the special operating conditions pointed out, and for this reason the carburetors are generally provided with special devices, one for feeding at the minimum speed, another for feeding in the start period and further, if needed, an accelerator pump. In certain cases the device for feeding at the minimum speed is provided with aa auxiliary device intended to suppress its action when the engine acts as a motor-brake. However said devices, which are substantially independent from each other, considerably complicate the structure of the carburetor, and moreover, in the presently known embodiments, these devices are not capable of supplying to the engine a mixture homogeneous enough and correctly proportioned, whereby, when they are operative, the engine still runs with relatively high consumption and low efficiency, and it gives rise to considerable ambient pollution.
More particularly, the device for feeding at the minimum speed is generally embodied by an outlet which delivers gasoline in the intake conduit downstream the carburetor shutter. The thus introduced gasoline cannot pulverize and vaporize enough before it comes to the engine cylinders. The device for start has a structure similar to that now described of the device for feeding at the minimum speed, and then it shows similar drawbacks, or even it comprises a special little additional carburetor, but this is an excessively complicated and expensive solution. The accelerator pump, when foreseen, requires complicated mechanical or pneumatic devices for its actuation, and moreover it supplies the gasoline at a very low pressure and therefore in conditions unsuitable for an effective pulverization.